1. Field of the Invention
This invention relates to a method of and an apparatus for producing a composite member of light alloy and porous materials or fiber of metal and/or inorganic material or a molded body of such porous materials or fiber.
2. Description of the Related Art
Because of its light weight and high heat conductivity, aluminum alloy has been in wide use for a material of automotive engine parts. However the aluminum alloy is disadvantageous in that it is inferior to iron materials such as cast iron or steel in heat resistance and/or wear resistance. Accordingly, for example, in a piston for a diesel engine, it has been proposed to reinforce the top ring groove, which should be high in wear resistance, by forming the periphery of the groove by a composite material of aluminum alloy and a porous material of metal such as nickel (Japanese Patent Publication No. 2(1990)-30790) or by a composite material of aluminum alloy and inorganic fiber such as alumina-silica fiber (Japanese Patent Publication No. 3(1991)-62776). Further in Japanese Unexamined Patent Publication No. 63(1988)-53225, there has been disclosed an engine cylinder sleeve formed of aluminum alloy reinforced with inorganic fiber.
In forming the reinforced portion by composite material, a high-pressure casting method is employed to impregnate the pores of a porous metal preform or an inorganic fiber preform with molten aluminum alloy. That is, a reinforcing material preform having a predetermined porosity is set in a casting mold, molten aluminum alloy is cast in the mold and then a pressure of about 300 to 1500 Kg/cm.sup.2 is applied to the molten aluminum alloy by a mechanical means such as a pressure punch or plunger. The pressure is held until the molten aluminum alloy is solidified.
However this method involves the following problem due to a high pressure.
A large and expensive apparatus is necessary. A pressurizing mechanism for applying a high pressure or a strong mold clamping mechanism is necessary.
It is hard to use a disintegrating core such as a salt core or a sand core. That is, molten metal can soak into the core or the core can be deformed or broken by the high pressure.
The degree of freedom in shape of the product is low. That is, since the metal mold must withstand a high pressure, the structure of the mold is limited, and accordingly it is hard to manufacture a product of a complicated shape or of a large size.